Aspiration Pneumonia

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Aspiration Pneumonia

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Aspiration pneumonia results from inhalation of stomach contents or secretions of the oropharynx, leading to lower respiratory tract infection. In many healthy adults, very small quantities of aspiration occur frequently but the normal defence mechanisms (cough, lung cilia) remove the material with no ill effects. However, aspiration may cause:

Chemical pneumonitis: chemical irritation of the lungs, which may progress to acute respiratory distress syndrome and/or bacterial infection. Acute aspiration of gastric contents into the lungs can produce an extremely severe and sometimes fatal illness. This has been termed Mendelson's syndrome and can complicate anaesthesia, particularly during pregnancy.

Obstruction: large volumes of aspirated material may lead to obstruction of the respiratory tract.

Bacterial infection: infection of the lower airways may lead to empyema, lung abscess, acute respiratory failure and acute lung injury. Persistent aspiration pneumonia is often due to anaerobes and it may progress to lung abscess or even bronchiectasis.

The usual site for an aspiration pneumonia is the apical and posterior segments of the lower lobe of the right lung. If the patient is supine then the aspirated material may also enter the posterior segment of the upper lobes.

Epidemiology

It is common. One study of elderly patients implicated aspiration pneumonia in 10% or cases of community-acquired pneumonia[1].

Aspiration pneumonia is relatively common in hospital and usually involves infection with multiple bacteria, including anaerobes.

It is more common in men, young children and the elderly.

Pathogens

Pathogens of community-acquired aspiration pneumonia are often the normal flora of the oropharynx, including:

Streptococcus pneumoniae.

Staphylococcus aureus.

Haemophilus influenzae.

Anaerobes - eg, Peptostreptococcus, Fusobacterium and Prevotella spp.

'Streptococcus milleri' group.

Klebsiella pneumoniae - increasingly seen in those with a history of alcohol misuse.

In the absence of a tracheo-oesophageal fistula, significant aspiration usually occurs only during periods of impaired consciousness, with reflux oesophagitis with an oesophageal stricture, or in bulbar palsy. The following are considered to be independent risk factors for aspiration pneumonia:

Mechanical obstruction: removal of the object, normally by bronchoscopy.

Tracheal suction if seen early.

Intubation with positive pressure ventilation may be required.

Bacterial infection of lower airways (the choice of antibiotics will be influenced by any recent previous antibiotic treatment, microbiology culture results and the patient's condition):

Initial empirical antibiotic therapy while awaiting culture results.

Antimicrobial therapy should be based on the patient's characteristics, the setting in which aspiration occurred, the severity of pneumonia, and available information regarding local pathogens and resistance patterns[6].

Community-acquired aspiration pneumonia is often initially treated with co-amoxiclav. Metronidazole may need to be added if there is evidence of complications - eg, lung abscess. See separate Pneumonia article for indications for hospital admission[2].

Hospital-acquired aspiration pneumonia: a suitable combination in patients who have already recently been treated with antibiotics is piperacillin with tazobactam.

The role of steroids is uncertain and not of proven benefit.

Supportive therapy with fluid management, bronchodilators and physiotherapy may help.

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